Cells of the renal medulla are highly specialized to function in the adverse environment of hyperosmotic stress. Work in the Sponsor's laboratory has shown that specific signal transduction and gene expression events enable inner medullary collecting duct (IMCD) cells to survive this stress. Moreover, IMCD cells are known to be relatively resistant to nephrotoxic injury. Nonetheless, the molecular responses of renal epithelial cells to nephrotoxic injury are poorly defined. This proposal aims to define the cellular and molecular mechanisms responsible for this enhanced injury resistance in order to gain insights regarding alternative therapeutic options. The project will make use of HT cells, a cell line chronically adapted hyperosmolality, have a stress resistant phenotype, reflecting altered. gene expression. The Specific Aims of this proposal-are: 1) Characterize the ability of HT and mIMCD3 cells to exhibit tolerance when exposed to nephrotoxic stress. 2) Characterize the ability of stress proteins to confer tolerance of nephrotoxins. 3) Identify functionally related gene families that effect survival or apoptosis under stress stimulation using cDNA arrays to perform large-scale analysis of differential mRNA expression. Overall, this project will advance our understanding of molecular mechanisms involved in acquiring stress tolerance and also enable the applicant to acquire new research skills and experience that will be critical for becoming an independent investigator.